In reply to Shiremog,
Don't believe the figures, just do the sums - power to weight ratio in standard trim will give you the answer, best part of 300 bhp for the 3.7 litre v circa 240 bhp per tonne for the 3 litre. If you felt you needed still more the engine is good for more horses for minimal expense with some very minor mods one could add 10 percent to the output, this puts the 3.7 Roadster bhp per tonne equal to the plus 8 which is quoted at a very believable 4.5 seconds for the dash to 60 - no slouch and a genuine 911 botherer if you are so inclined.
I am sure the quoted figures reflect a need to market the plus 8 as a significantly quicker car. Having said that both cars are very different animals.
Enjoy your car, get some miles on the engine, and I'm sure you will find performance is by no means lacking.